Engineering mechanics

Students Learn About:

simple machines
static friction

– concept of friction and its application in engineering

coefficient of friction

– normal force

– friction force

– angle of static friction

– angle of repose

basic calculations for work, energy and power

– potential energy

– kinetic energy

Students Learn To:

apply mathematical and/or graphical methods to solve engineering problems related to transport including mechanical advantage, velocity ratio and efficiency
analyse problems involving static friction
differentiate between the concepts of energy and power and apply appropriate basic calculations

Terminology:

Mechanical Advantage, Velocity Ratio, Efficiency, Static Friction, Kinetic Friction, Normal Force

Introduction

When we know the Mechanical Advanatge and Velocity Ratio, we are able to calculate how efficent a simple machine is. For many examples leading up to this we have assumed that the efficency is 100%. This means no energy has been wasted on heat, friction, or sound.

Using the methods below we can begin to calculate all three of these in less than 100% efficent systems with plug and play. But to follow the math lets break down the concepts and ensure we know WHY each part matters and how it relates to the others.

Longer video, watch the ones below first, this would be your back up.

MA1

Summarise mechanical advatages, and the various ways to proof it

MA2

A follow through of mechanical advantage, alternate explanation of how it is working

MA - Wheel & Axel

MA + VR + Efficiency

This video, everything happens very quickly at the end! stay with it 👍🏻

What Is Friction

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Friction is desirable and important in supplying traction to facilitate motion on land. Most land vehicles rely on friction for acceleration, deceleration and changing direction. Sudden reductions in traction can cause loss of control and accidents.

Normal Force

The normal force is something that creates a great deal of confusion. It is not the weight force, which is an important point to understand. The normal reaction is a perpendicular reaction, provided by the surface on which the object is resting.

What is the characteristic of the weight force? What is the characteristic of the normal reaction?

Friction Force

Two things determine the friction force, or the frictional resistance, the force resisting the tendency towards motion between surfaces. They are the coefficient of friction between the surfaces, and the normal reaction. The higher the coefficient of friction, the higher the frictional force will be. If, however, the surfaces have a low coefficient of friction then a higher normal reaction is needed to get a high frictional force. For example, in a car the normal reaction is controlled by the mass, so good friction between the tyres and the road is dependant on the coefficient of friction between the surfaces.

Coefficent Of Friction

The friction coefficient is an empirical (experimentally measured) structural property that depends only on various aspects of the contacting materials, such as surface roughness. The coefficient of friction is not a function of mass or volume. For instance, a large aluminum block has the same coefficient of friction as a small aluminum block. However, the magnitude of the friction force itself depends on the normal force, and hence on the mass of the block.

The coefficient of friction (COF), often symbolized by the Greek letter µ, is a dimensionless scalar value which equals the ratio of the force of friction between two bodies and the force pressing them together, either during or at the onset of slipping. The coefficient of friction depends on the materials used; for example, ice on steel has a low coefficient of friction, while rubber on pavement has a high coefficient of friction. Coefficients of friction range from near zero to greater than one. It is an axiom of the nature of friction between metal surfaces that it is greater between two surfaces of similar metals than between two surfaces of different metals— hence, brass will have a higher coefficient of friction when moved against brass, but less if moved against steel or aluminum

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